cavity filters， cst

For cavity filter design, now we only first simulate single cavity's resonance frequency, then caculate the coupling coefficient that determine the ires'width.
I have seen some papers that introduce full cavity filter simulation using HFSS and CST,but I can't grasp the main idear,
Can anyone introduce some method on full filter simulation in detail.
Thanks
The attached is the pic on filter synthesis programe

Here you full method for cavity filter simulation in CST:
http://www.cst-china.cn/application.asp?path=62&id=102
ps. at the end of posted page you have link> next step, there are 7 pages in all.

goxy
Thanks for your answer
But the filter that I design include tuning and coupling screw, so more parameters need to be determined,and if use crosscoupling then how to do?

en, not a hard work...
in theory at least...